In the Linux kernel, the following vulnerability has been resolved:

ext4: fix timer use-after-free on failed mount

Syzbot has found an ODEBUG bug in ext4_fill_super

The del_timer_sync function cancels the s_err_report timer,
which reminds about filesystem errors daily. We should
guarantee the timer is no longer active before kfree(sbi).

When filesystem mounting fails, the flow goes to failed_mount3,
where an error occurs when ext4_stop_mmpd is called, causing
a read I/O failure. This triggers the ext4_handle_error function
that ultimately re-arms the timer,
leaving the s_err_report timer active before kfree(sbi) is called.

Fix the issue by canceling the s_err_report timer after calling ext4_stop_mmpd.

kernel.org https://git.kernel.org/stable/c/0ce160c5bdb67081a62293028dc85758a8efb22a [No types assigned]

kernel.org https://git.kernel.org/stable/c/9203817ba46ebba7c865c8de2aba399537b6e891 [No types assigned]

kernel.org https://git.kernel.org/stable/c/b85569585d0154d4db1e4f9e3e6a4731d407feb0 [No types assigned]

kernel.org https://git.kernel.org/stable/c/fa78fb51d396f4f2f80f8e96a3b1516f394258be [No types assigned]